Auxiliary drive unit for an actuator



y 8, 1968 P. T. M. NOTT 3,385,120

AUXILIARY DRIVE UNIT FOR AN ACTUATOR Filed July 6, 1966 2 Sheets-Sheet lINVENTOR Te N 077 May 28, 1968 P. T. M. NOTT 3,385,120

AUXILIARY DRIVE UNIT FOR AN ACTUATOR Filed July 6, 1966 2 Sheets-Sheet 2INVENTOR Peter Norr TTORNEYS United States Patent 3,385,120 AUXHJARYDRIVE UNIT FOR AN ACTUATOR Peter Thomas Mence Nott, Ingatestone, Essex,England, assignor to Rotork Engineering Company Limited, Bath, England,a British company Continuation-impart of application Ser. No. 330,964,Dec. 16, 1963. This application July 6, 1966, Ser. No. 563,258

Claims. (Cl. 74107) This application is a continuation-in-part of U.S.patent application Ser. No. 330,964, filed Dec. 16, 1963, now abandoned,and relates to an auxiliary drive unit for an actuator, moreparticularly, but not exclusively, for the operation of valves. Theinvention is particularly applicable to conventional valve actuators,for example, actuators of the kind described in our British patentspecifications Nos. 842,581 and 865,565. In these prior arrangements thevalve or other apparatus is normally actuated by the axial travel of thevalve spindle in response to rotation of the driving nut of theactuator. The torque exerted by such prior arrangements remains constantthroughout the travel of the valve spindle and this has proved asatisfactory arrangement particularly for rising spindle valves.However, with plug valves or butterfly valves which are angularlymovable, e.g. through 9, from their open to their closed position, it isobvious that a greater torque is desirable from the actuator as thevalve approaches and reaches its closed position. It is therefore anobject of the invention to provide an improved actuator which is capableof exerting a variable torque so as to apply a greatly increased torqueon the valve member in a desired position, for example, at its closedposition.

In its broadest aspect the invention provides an auxiliary drive unitcomprising a casing, an input member positioned in said casing for axialor rotary movement therein, an output shaft, one Or more arms mounted onsaid output shaft and movable therewith, a cam slot formed in each armwith each cam slot located at an angle to the radial axis of itscorresponding arm, and a cross pin carried by the movable input memberand mounted in said cam slot or slots so as to translate linear movementof the input member into a predetermined angular movement of the outputshaft having a variable torque output. The angular location of each camslot is relative to the radial axis of the arm as defined with referenceto the output shaft of the auxiliary drive unit.

The invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 is a front elevation showing a unit in accordance with theinvention, the cover plate being removed so as to show the operatingparts more clearly;

FIG. 2 is an end elevation of the unit shown in FIG. 1, the figure beingpartly in section on the line 22 of FIG. 1 so as to show the relativeposition of the operating parts when the output shaft has reached itshalfway position;

FIG. 3 is a front elevation showing an alternative embodiment of theunit of the present invention with the cover plate removed; and

FIG. 4 is a partial front elevation showing an alternate form of theslot 74 of FIG. 3.

As previously mentioned, the unit of the present invention isparticularly applicable for attachment as a selfcontained unit to theoutput of conventional valve actuators, e.g., actuators of the kinddescribed and claimed in our British patent specifications Nos. 842,581and 865,565. In the embodiment of FIGS. 1 and 2, a threaded spindlewhich may be the output shaft of the actuator is shown by the reference11 and this is coupled with the Ice unit 12 of the present invention soas to extend into an aperture 13 whereby the output shaft 11 of theactuator will extend and move transversely across the casing 14. Theshaft 11 is coupled at its inner end with a block 15 which rotatablysupports a transverse cross pin 16 having rollers 17 rotatably mountedon each of its ends. The casing 14 of the unit 12 is provided with apair of opposed longitudinally extending slots 18 which provide guidesor runways for the rollers 17 on the cross pin 16. The rollers therebysupport the inner end of the shaft 11 of the actuator so that during itsaxial movement, the rollers 17 will move along the slots 18 until theblock 15 reaches the inner limit of its travel which is determined bythe adjustable screw 19 mounted in the end plate 20 and secured by thenut 21.

The output shaft of the unit is indicated by the reference 22 and itwill be seen that this shaft is located at right angles to the shaft 11of the actuator and is disposed at the side of it in an extension 23 ofthe main casing. As shown in FIG. 1 the output shaft is keyed, forconvenience of manufacture, to a sleeve 24 which surrounds the shaft 22within the casing 23. A pair of spaced radially extending arms 25 areformed integrally with a boss 26 connected with the sleeve 24 by the key27 whereby angular movement of the arms 25 rotates the shaft 22. Axialmovement of the sleeve 24 in one direction is prevented by the lockingmeans 28 attached to the sleeve 24 and abutting boss 26, and in theother direction by a shoulder (not shown) on sleeve 24 abutting theother side of boss 26.

The radially extending arms 25 are positioned to extend into the casing14 one on each side of the block 15 on the shaft 11. The casing 14 issuitably shaped as at 29 to permit the movement of the arms 25 throughan angle of approximately 90 as indicated by the chain lines 30 inFIG. 1. This movement is obtained by providing each of the arms with acam slot 31 which has a width corresponding approximately to thediameter of the cross pin 16 which whereby extends snugly through theslots as shown in full lines in FIG. 1. The length of each of the slots31 is such as to permit the cross pin 16 to roll along it due to axialtravel of the shaft 11. As shown in FIG. 1, the cam slots 31 arepreferably located at an angle to the radial axis of the arms 31. Theangular deviation depends on the operating characteristics of the unitas will be hereinafter explained, but may be of the order of 20 to 30.In FIG. 1 each cam slot 31 is located at 20 to the radial axis of itsarms 25.

It will be appreciated that by suitably fitting the auxiliary drive unitof the invention to an actuator, considerable variation in the outputtorque can be obtained in relation to the axial movement of the actuatoroutput shaft 11. As previously mentioned, the torque exerted by thetravel of the shaft 11 remains constant throughout its travel and thisis a satisfactory arrangement for rising spindle valves. The presentinvention is particularly useful for operating plug valves or butterflyvalves which are angulariy movable and where a greater torque isdesirable as the valve reaches its closed position. As shown in theembodiment of FIG. 1, the valve operating shaft 22 is in the valve openposition and as the shaft 11 moves axially towards the limit screw 19,the cross pin 16 will exert a force on the arms 25 rotating the shaft22. During this movement the cross pin 16 rolls along the cam slots 31until it reaches the position shown by dotted lines and indicated by thereference A, which time the valve has reached its half shut position(i.e., It will be appreciated that in moving the valve to its half shutposition the shaft 11 has not moved through half of its axial travel andthis is, of course, due to the angular positioning of the slots 31 withrespect to the radial axis of the arms 25. As a result, a much greatertorque output is available during the further axial movement of theshaft 11 in order to move the shaft 22 through the final 45 to close thevalve. The final position of the operating parts is shown by the dottedlines indicated by the reference B and it will be seen that the crosspin has now returned along the cam slots 31 to a final position which isdetermined by the abutment of the block with the limit screw 19.

As shown in FIG. 2 of the drawings, the output shaft 22 of the unit issupported by a bearing 32 in an aperture 33 extending from the casingsection 23. The cover 34 (shown only in FIG. 2) may be provided with aninspection window (not shown) or any other suitable mechanical orelectrical device for indicating or permitting the position of theoutput shaft 22 to be ascertained. For example, the outer end of theoutput shaft 22 may be provided with an indicating device such as anarrow which could be viewed through an inspection window so as to allowthe operator to ascertain the exact position of the valve beingoperated.

The modified arrangement as shown in FIG. 3 includes a threaded inputshaft 42 which extends across the casing 43 of the unit and isrestrained against axial movement as will be hereinafter explained. Theend 44 of the shaft 42 is mounted in a bearing shown generally by thereference numeral 45 and the other end 46 of the shaft extends throughan aperture 47 in the casing 43 and is connected with the output of theactuator 41.

The output secton of the actuator 41 comprises a rotatable output shaft48 supported by a lower thrust bearing 49 mounted in the casing 50 ofthe actuator. A rotatable nut member 51 is slidably mounted within theend of the actuator output shaft 48, and is formed with a flange 52which abuts and seats on the lower end surface of shaft 42. The edge ofthe actuator output shaft 48 at its lower end is formed with a pair ofprojections or dogs which are located diametrally opposite to each otherand which extend axially into corresponding slots (not shown) in theflange 52 of the nut member 51. The drive from the actuator output shaft48 is always transmitted to the rotatable nut member 51 through thedogs, but the axial force is contained by a short outer sleeve 53 whichthreadably engages the lower end of the actuator output shaft 48 and isflat at its lower end to firmly engage the flange 52 of the nut member51 with the lower end of the actuator output shaft 48.

In the assembly of the present invention, the rotatable nut 51 ismounted on the end 46 of the threaded shaft 42 and is secured thereon bymeans of a pair of lock nuts 54 which engage the threaded end of theshaft 42. The lock nuts 54 engage a washer 55 and a bush 56 is providedbetween the rotatable nut member 51 and the washer 55. The rotatable nutmember 51 is keyed to the shaft 42 by means of the key 57 so thatrotation of the actuator output shaft 48 produces a correspondingrotation of the threaded shaft 42 of the auxiliary drive unit 40.

The provision of the rotatable nut member 51 as part of the motiontransmitting mechanism between the actuator output shaft 51 and thethreaded input shaft 42 of the auxiliary drive unit provides a verysimple mounting which permits changes in the capacity of the shaft 42without affecting the actuator construction. It will be appreciated thatany variations in the shaft 42 can be accommodated by merely changingthe size of the rotatable nut 51. This can be done without affecting thesize of the actuator.

The bearing 45 for the other end 44 of the threaded shaft 42 extendswithin an aperture 58 at the other end of the casing 43 and the bearinforms part of a closure plate 59 which is attached to the casing bybolts 60. The closing plate 59 has a central recess for accommodating alock nut 61 attached to the threaded end 44 of the shaft 42. As shown,the lock nut is split at 62 for a portion of its periphery and aftermounting on the shaft the split portions are firmly held together by thescrew 63 which positively retains the lock nut 61 in position on theshaft.

It will be appreciated that the threaded shaft 42 is rotatably supportedacross the casing 43 of the auxiliary drive unit 40 and it is restrainedagainst axial movement. The shaft 42 is always in tension irrespectiveof the direction of drive imparted to it by the output shaft of theactuator 41. This arrangement has the advantage of permitting areduction in the diameter of the shaft 42 and this is valuable becauseit increases the efficiency of the screw thread and reduces the inputtorque necessary for a given output.

An input member in the form of a block or nut 64 is threadably mountedon the input shaft 42 for axial movement thereto in response to rotationof the shaft. The nut 64 forms part of a transverse cross pin on whichrollers 66 are rotatably mounted, via pair of intermediate rollers 68,for movement in a pair of opposed longitudinally extending slots 67formed in the casing as in the embodiment of FIGS. 1 and 2. In theembodiment of FIG. 3, these slots 67 also prevent any rotation of thenut 64 with the shaft 42. As in the first embodiment, a pair of arms 71are provided on either side of the nut 64, each of said arms having aslot 74 in which intermediate rollers 68 slide due to the axial travelof nut 34 on shaft 12. Arms 71 are coupled to output shaft in the samemanner as in the first embodiment of FIGS. 1 and 2, and the valve openand closed positions of the operating parts is predetermined by means ofthe adjusting screws 76 located in the casing and which are adapted toabut one of the arms 71. The remaining structure of the embodiment ofFIG. 3 is similar to that of the embodiment of FIGS. 1 and 2 andtherefore will not be described again in detail.

In the operation of the embodiment of FIG. 3, rotation of the actuatoroutput shaft 48 is imparted to shaft 42 causing axial travel of nut 64on shaft 42 and therefore a movement of intermediate rollers 38 in slots74 of arms 71 to move the latter and cause rotation of output shaft 80exactly as described in the embodiment of FIGS. 1 and 2.

The unit of FIG. 3 can also be operated as a self-contained drive unitin which case a suitable handwheel can be mounted on the end 46 of theshaft 42. In such an arrangement this end would be supported in abearing forming part of an end cover plate secured to the casing 43 Bothof the embodiments described above provide for a considerable torqueincrease in the latter stages of closing a valve. It will, however, beappreciated that many modifications can be made and in some cases acurved slot can be used so as to give a torque variation to meet aparticular requirement. Such an arrangement is shown in FIG. 4 in whicha curved slot 74' is shown formed in arm 71' It is also within the scopeof the invention to provide a radially positioned slot with respect tothe axis of the arms 25 and 71. It will be appreciated that with such aslot the torque output would increase at each end of the stroke of theinput shaft or nut, thus assisting the final movement of the valve intoits open and closed positions.

It will be further appreciated that the invention is ideally suitablefor attachment as a completely self-contained unit to a conventionalactuator as normally used for rising spindle valves. The support of theoperating parts and, in particular, the input members by the rollers inthe slots, enables any side thrust to be transmitted through the rollersdirectly to the casing, so that there is no load on the thread.

Of course variations of the specific construction and arrangement ofthis type mechanism herein disclosed can be made by those skilled in theart without departing from the invention as defined in the appendedclaims.

In the claims:

1. An auxiliary drive unit comprising a casing having a pair oflongitudinally extending slots; an input member positioned in saidcasing for reciprocal movement therein; a pair of cross members mountedon said input member and extending at right angles thereto, said crossmembers being movable between a starting position and an ending positionrespectively located adjacent each end of said casing upon said movementof said input member; a roller rotatably mounted on each of said crossmembers and riding in a corresponding slot; an output shaft rotatablymounted in said casing, said output shaft having its longitudinal axislocated in a plane transverse to the direction of movement of said inputmember, said plane passing through the midpoint of said two positions; asleeve removably mounted over and engaging said output shaft; a pair ofarms each having a longitudinal axis extending radially with respect tosaid output shaft; one end of each of said arms engaging said sleeve,and the other end of each of said arms being provided with a cam slot inwhich a corresponding cross member extends to transmit linear movementof said input member to rotary movement of said output shaft; said camslots extending at an angle with respect to the longitudinal axis ofsaid arms so that a greater torque is exerted on said output shaftduring movement of said input member from said midpoint to said endingposition, than from said starting position to said midpoint; and meansto adjustably limit said movement.

2. The drive unit of claim 1 wherein said input member comprises aninput shaft axially movable in said housing.

3. The drive unit of claim 2 wherein said means to adjustably limit saidmovement comprises a limit screw adjustably mounted in one end of saidcasing for determining one end position for the axial movement of theinput shaft and cross members carried thereby.

4. The drive unit of claim 2 wherein the input shaft is provided with anend block supporting said cross members.

5. The drive unit of claim 1 further comprising an input shaft rotatablymounted in said casing, and wherein said input member includes a nutthreadably mounted on said input shaft so as to move axially in responseto rotation of said input shaft in any direction.

6. The drive unit of claim 5 wherein said means to adjustably limit saidmovement comprises at least one limit screw adjustably mounted in saidcasing and adapted to abut one of said arms.

7. The drive unit of claim 5 wherein said cross members compriseintermediate rollers rotatably mounted on said nut.

8. The drive unit of claim 5 in which the input shaft is restrainedagainst axial movement by thrust bearings mounted one at each end ofsaid casing so that said input shaft is maintained in tension.

9. The drive unit of claim 1 wherein said angle is between 20 and 30.

10. The drive unit of claim 1 wherein each of the cam slots is curvedwith respect to the radial axis of its arm.

References Cited UNITED STATES PATENTS 2,908,182 10/1959 Bacchi 74-5092,930,252 3/1960 Sears et a1. 74509 3,063,298 11/1962 Elliott 74-509 XMILTON KAUFMAN, Primary Examiner.

1. AN AUXILIARY DRIVE UNIT COMPRISING A CASING HAVING A PAIR OFLONGITUDINALLY EXTENDING SLOTS; AN INPUT MEMBER POSITIONED IN SAIDCASING FOR RECIPROCAL MOVEMENT THEREIN; A PAIR OF CROSS MEMBERS MOUNTEDON SAID INPUT MEMBER AND EXTENDING AT RIGHT ANGLES THERETO, SAID CROSSMEMBERS BEING MOVABLE BETWEEN A STARTING POSITION AND AN ENDING POSITIONRESPECTIVELY LOCATED ADJACENT EACH END OF SAID CASING UPON SAID MOVEMENTOF SAID INPUT MEMBER; A ROLLER ROTATABLY MOUNTED ON EACH OF SAID CROSSMEMBERS AND RIDING IN A CORRESPONDING SLOT; AN OUTPUT SHAFT ROTATABLYMOUNTED IN SAID CASING, SAID OUTPUT SHAFT HAVING ITS LONGITUDINAL AXISLOCATED IN A PLANE TRANSVERSE TO THE DIRECTION OF MOVEMENT OF SAID INPUTMEMBER, SAID PLANE PASSING THROUGH THE MIDPOINT OF SAID TWO POSITIONS; ASLEEVE REMOVABLY MOUNTED OVER AND ENGAGING SAID OUTPUT SHAFT; A PAIR OFARMS EACH HAVING A LONGITUDINAL AXIS EXTENDING RADIALLY WITH RESPECT TOSAID OUTPUT SHAFT; ONE END OF EACH OF SAID ARMS ENGAGING SAID SLEEVE,AND THE OTHER END OF EACH OF SAID ARMS BEING PROVIDED WITH A CAM SLOT INWHICH A CORRESPONDING CROSS MEMBER EXTENDS TO TRANSMIT LINEAR MOVEMENTOF SAID INPUT MEMBER TO ROTARY MOVEMENT OF SAID OUTPUT SHAFT; SAID CAMSLOTS EXTENDING AT AN ANGLE WITH RESPECT TO THE LONGITUDINAL AXIS OFSAID ARMS SO THAT A GREATER TORQUE IS EXERTED ON SAID OUTPUT SHAFTDURING MOVEMENT OF SAID INPUT MEMBER FROM SAID MIDPOINT TO SAID ENDINGPOSITION, THAN FROM SAID STARTING POSITION TO SAID MIDPOINT; AND MEANSTO ADJUSTABLY LIMIT SAID MOVEMENT.